How to balance lethality.

Ok so basically how lethality has been all season is either weak as hell or way too op. Right now its in one of those op states but not because of lethality itself, as i think its balanced and actually quite needed on assassins. Assassins have to get right in your face to do any damage and risk getting blow up by your entire team in teamfights. That's the trade-off for being able to ridiculous damage. Assassins really need lethality or they just become trash tier. the problem is that when goes in to assassinate a squishy, he risks getting cc'd and then blown up by an entire team and becoming useless altogether. Assassins are risky champions that are rewarded for doing good. so why is it that can do more damage then from behind the rest of her team, at no risk of being killed. Its dumb and unhealthy for the game. Just either make lethality items melee only or make then 50% effective on adcs. Otherwise adcs will abuse lethality and then the whole stat will get nerfed putting assassins in the dumpster again.